This invention relates to an optical sensor for use in optical measurement.
Recently, optical components such as laser diodes, detector, and optical fibers have been developed intensively. As they are advanced in performance, high precision optical measurements by using optical sensor can be realized. These components are attracting wide attention owing to their advantages, such as freedom from electromagnetic induction noise, high insulation, and low loss of optical fiber. In particular, attempts have been made to widely use optical magnetic (current) sensors in high voltage cables or the like by making use of such advantages.
FIG. 1 shows a system configuration of an optical magnetic sensor. The light from a light source 101 provided in an optical transmitter 100 enters a sensor unit 103 by way of an optical fiber 102. The magnetic field intensity is converted into an optical intensity in the sensor unit 103, and the light runs again through the optical fiber 102, and is converted into an electric signal at a detector 104 provided in an optical receiver 105. Then, the signal is processed in the signal processing unit. The sensor unit 103 is mainly composed of a polarizer 107, a magnetic optical crystal 108, and an analyzer 109.
FIG. 2 shows the composition of a conventional sensor unit. The light passed through a polarizer 201 becomes a straight polarized light, and it passes through a magnetic optical crystal 202 having a certain length, and at this time the plane of polarization is rotated by an angle .theta. proportional to the optical path length and external magnetic field. The angle of rotation .theta. is converted into an optical intensity by an analyzer 203 disposed at an angle of 45 degrees to the polarizer 201. The quantity of light after passing through the analyzer 203 is proportional to the angle of rotation .theta..
The thus described sensor unit, however, involves the following problems. The sensor unit is composed of a crystal 202 having a magnetic optical effect, a flat plate polarizer using rutile or the like (polarizer 201, analyzer 203), prism 204, rod lens 205 and others, which means that there are too many component parts. Accordingly, (1) it is very difficult to match the optical axia at high precision, (2) when adhering the individual parts by thermoset adhesive or the like, it is necessary to fix the optically adjusted parts for a long time at high temperature, and it is likely that the optical axis becomes deviated at this time, (3) the adhesive is poor in reliability, and peeling may occur when used for a long time, and (4) mass production is difficult because each part must be individually adhered.